itersolve: Use stricter completion check in itersolve_find_step()

Use a more strict check for determining if the iterative solver has
correctly found a step - the guess must be within 1 picometer of the
target or correct to within 1 nanosecond.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

1 files changed, 4 insertions, 2 deletions

diff --git a/klippy/chelper/itersolve.c b/klippy/chelper/itersolve.c
index ae351f7d..36f9ea90 100644
--- a/klippy/chelper/itersolve.c
+++ b/klippy/chelper/itersolve.c
@@ -43,11 +43,11 @@ itersolve_find_step(struct stepper_kinematics *sk, struct move *m
     for (;;) {
         double guess_time = ((low.time*high.position - high.time*low.position)
                              / (high.position - low.position));
-        if (fabs(guess_time - best_guess.time) <= .000000001)
-            break;
         best_guess.time = guess_time;
         best_guess.position = calc_position_cb(sk, m, guess_time);
         double guess_position = best_guess.position - target;
+        if (fabs(guess_position) <= .000000001)
+            break;
         int guess_sign = signbit(guess_position);
         if (guess_sign == high_sign) {
             high.time = guess_time;
@@ -62,6 +62,8 @@ itersolve_find_step(struct stepper_kinematics *sk, struct move *m
                 high.position *= .5;
             prev_choice = -1;
         }
+        if (high.time - low.time <= .000000001)
+            break;
     }
     return best_guess;
 }